apex: checks min_sdk_version for preview/current

If we don't check "current", it won't be checked even in the finalized
branch.

If we don't check "preview", it should be done during the SDK
finalization. It'd be better done before the SDK finalization regarding
that setting min_sdk_version is to get approval from deps library owners.

Bug: 177833148
Test: m (soong tests)
Change-Id: I712b61cfe5a134fbb69c73956d26fb3a1e5c011e

apex/builder.go

@@ -598,7 +598,7 @@ func (a *apexBundle) buildUnflattenedApex(ctx android.ModuleContext) {
 
 		// bundletool doesn't understand what "current" is. We need to transform it to
 		// codename
-		if moduleMinSdkVersion.IsCurrent() {
+		if moduleMinSdkVersion.IsCurrent() || moduleMinSdkVersion.IsNone() {
 			minSdkVersion = ctx.Config().DefaultAppTargetSdk(ctx).String()
 		}
 		// apex module doesn't have a concept of target_sdk_version, hence for the time